Heat sink for cooling a heat producing element and application

ABSTRACT

A heat sink mounted on a heat producing element for cooling the heat producing element attached on the printed board of the electronic apparatus, having a heat sink body made of a good heat conductive material and a fan assembly installed inside the heat sink body. The heat sink body is efficiently air-cooled by a cooling air generated by the rotation of the fan assembly. The cooling air forcibly cools a base and a fixing wall of the base adjacent to the heat producing element and plate-like radiating fins or a pin-like radiating fins are protruded on the heat sink body to radiate the heat effectively. The position of the fan assembly is at the center of the heat sink body or is at the offset position from the center of the heat sink body. The heat sink of the present invention can be installed in a portable electronic apparatus such as a portable computer.

This is a divisional of application Ser. No. 08/433,131 filed May 3,1995, now U.S. Pat. No. 5,504,650 which is a continuation of applicationSer. No. 08/067,084 filed May 26, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a heat sink for cooling a heatproducing element by being mounted on the top face thereof, especially,the present invention relates to the heat sink having a fan assemblyattached inside of its body and forcibly cooling a heat producingelement with a cooling air generated by the rotation of the fanassembly.

2. Description of the Related Art

Among electronic devices, such as transistors and integrated circuits,it is not necessary for a device consuming a small quantity of currentto radiate of heat produced therein, since the amount of heat producedtherefrom is small. On the contrary, devices handling a large quantityof current, such as power transistors and integrated circuits for poweramplifiers in audio equipment or a current booster in a constant voltagecircuit, a large amount of power turns to heat in accordance with theoperating state thereof and the device may break down when thetemperature of the device increases above the operating temperature.

As a countermeasure to this, a heat sink for cooling the element ismounted on the device producing a large quantity of heat. The heat sinkis usually made of a material having a good heat conductivity such asaluminum, and a set of radiating fins are disposed on the upper face ofthe heat sink. The heat sink is used in circumstances where cooling airis forcibly flowing and is adhered or mounted with pressure on the heatproducing element, and the heat produced at the element is transferredto the heat sink and absorbed by its body or dissipated by the flowingair.

However, when the amount of heat produced by the element increases, itis necessary to increase the flowing speed of the cooling air around theelement for increasing a cooling efficient, thereby it is required touse a powerful fan. The powerful fan generally requires an increase inthe size of the fan or an increase in the rotational speed of the fan,thereby causing an increase in the space for the powerful fan or anincrease in the noise generated by the powerful fan, as a result.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a heat sink that canrealize an efficiently cooling of a heat producing element withoutincreasing the packaging space thereof.

According to one aspect of the present invention, a fan assembly isdisposed inside a heat sink body made of material having a good heatconductivity, so that a fixing wall of the heat sink body positionednext to the heat producing element is forcibly cooled by the cooling airgenerated by the rotation of the fan assembly during the operation ofthe heat producing element.

According to another aspect of the present invention, a flowing route ofthe cooling air generated by the rotation of the fan assembly becomesvery efficient for cooling the heat sink body by modifying the shape ofa top plate of the heat sink body, the shape of a radiating fin of theheat sink body, or the installing position of the fan assembly, therebythe cooling efficiency of the fixing wall of the heat sink body isincreased within a limited inside space of the electronic apparatus.

Further, according to the present invention, it is possible to installthe heat sink in a portable electronic apparatus having a limitedinternal space, such as a portable personal computer or the like, bymodifying the top plate or the cover of the heat sink body.

In this way, the heat sink of the present invention realizes a efficientcooling of the heat producing element in a limited small space. Further,the manufacturing of the heat sink body becomes easy when the heat sinkbody is assembled by combining the base and the cover.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings, wherein:

FIG. 1 is a prior art structure of a heat sink;

FIG. 2 is a perspective assembly diagram showing a structure of the heatsink according to a first embodiment of the present invention;

FIG. 3 is a perspective view of the assembled heat sink in FIG. 2;

FIG. 4A is a sectional view of the heat sink in FIG. 3 showing an airflow of a cooling air;

FIG. 4B is a plan view of the heat sink in FIG. 3;

FIG. 5 is a perspective assembly diagram showing a structure of the heatsink according to a second embodiment of the present invention;

FIG. 6 is a perspective view of the assembled heat sink in FIG. 5;

FIG. 7 is a plan view of the heat sink in FIG. 6 showing an air flow ofa cooling air;

FIG. 8 is a perspective assembly diagram showing a structure of a coverand a base of the heat sink, and a manner of assembling according to athird embodiment of the present invention;

FIG. 9A is a plan view of the assembled heat sink having the cover andthe base in FIG. 8;

FIG. 9B is a sectional view taken on line B--B in FIG. 9A;

FIG. 10 is a bottom view of the assembled heat sink having the cover andthe base in FIG. 8;

FIG. 11 is a sectional view showing a structure of the heat sinkaccording to a fourth embodiment of the present invention;

FIG. 12A is a side view of the heat sink in FIG. 11;

FIG. 12B is a plan view of the heat sink in FIG. 11;

FIG. 13 is a perspective assembly diagram showing a modified structureof a cover and a base of the heat sink in FIG. 8, and a manner ofassembling according to the third embodiment of the present invention;

FIG. 14A is a plan view explaining a manner of assembling the cover onthe base in FIG. 13;

FIG. 14B is a side view of the base in FIG. 13;

FIG. 15 is a perspective assembly diagram showing another modifiedstructure of a cover and a base of the heat sink in FIG. 8, and a mannerof assembling according to the third embodiment of the presentinvention;

FIG. 16A is a plan view explaining a manner of assembling the cover onthe base in FIG. 15;

FIG. 16B is a side view of the cover in FIG. 15;

FIG. 17A is a perspective view of the cover in FIG. 8 having a pluralityof grooves crosswisely excavated on the top face;

FIGS. 17B and 17C are enlarged sectional view showing other shapes ofthe groove in FIG. 17A;

FIG. 18A is an explanatory view showing an air flow condition of thecooling air when the cover has grooves on the top face;

FIG. 18B is an explanatory view showing an air flow condition of thecooling air when the cover has no grooves on the top face;

FIG. 19A is a plan view of the cover in FIG. 8 having a plurality ofgrooves radially excavated on the top face thereof;

FIG. 19B is an enlarged perspective view of a part X in FIG. 19A;

FIG. 20A is a plan view of the cover in FIG. 8 having a plurality ofradiation pins on the top face thereof;

FIG. 20B is a side view of the cover in FIG. 20A;

FIG. 21 is a perspective assembly diagram showing a structure of a coverand a base of the heat sink, and a manner of assembling according to afifth embodiment of the present invention wherein radiation pins aredisposed on the bottom face of the cover;

FIG. 22 is a perspective plan view of the assembled heat sink having thecover and the base in FIG. 21;

FIG. 23A is an explanatory view showing an air flow condition of thecooling air when the cover has no radiation pins on the bottom facethereof;

FIG. 23B is an explanatory view showing an air flow condition of thecooling air when the cover has the radiation pins on the bottom facethereof;

FIG. 24A is a diagram showing a wind speed distribution when the coverhas the radiation pins on the bottom face thereof in comparison with thesame when the cover has no radiation pins on the bottom face thereof;

FIG. 24B is a diagram showing a characteristic between a wind speed anda heat resistance;

FIG. 25 is a perspective assembly diagram showing a structure of a coverand a base of the heat sink, and a manner of assembling according to asixth embodiment of the present invention wherein a fan assembly isdisposed offset to one of the side of the heat sink;

FIG. 26 is a perspective plan view of the assembled heat sink having thecover and the base in FIG. 25;

FIG. 27 is a perspective assembly diagram showing a structure of a coverand a base of the heat sink, and a manner of assembling according to aseventh embodiment of the present invention wherein a fan assembly isdisposed offset to one of the corner of the heat sink;

FIG. 28 is a plan view of the assembled heat sink having the cover andthe base in FIG. 27;

FIG. 29 is a partially cutaway view in perspective of a modifiedembodiment of the base in FIG. 27, wherein a space is provided byexcavating an upper bottom face of the base under the position of thefan assemly;

FIG. 30A is a plan view showing a modification of the base in FIG. 27wherein a distribution of the radiation pins are changed;

FIG. 30B is a sectional view taken on line Y--Y in FIG. 30A;

FIG. 31A is a plan view showing a modified embodiment of the coveraccording to the seventh embodiment of the heat sink in FIG. 27;

FIG. 31B is a side view of the cover in FIG. 31A;

FIG. 32A is an explanatory view showing one example of a manner ofmounting the heat sink on the heat producing element;

FIG. 32B is an explanatory view showing another example of a manner ofmounting the heat sink on the heat producing element;

FIG. 33A is a partial plan view showing a base mounted on the heatproducing element by using a heat sink fixture;

FIG. 33B is a partial side view of the base of the heat sink and theheat producing element in FIG. 33A fixed by the fixture;

FIG. 33C is a perspective view showing a structure of the heat sinkfixture in FIGS. 33A and 33B;

FIGS. 33D to 33F are perspective views showing other embodiments of theheat sink fixture;

FIG. 34 is an explanatory side view showing a structure for supplyingelectricity to the fan assembly according to one embodiment of thepresent invention;

FIG. 35 is an explanatory side view showing a structure for supplyingelectricity to the fan assembly according to another embodiment of thepresent invention;

FIG. 36 is a block diagram showing a fan assembly controller accordingto one embodiment of the present invention;

FIG. 37 is a sectional view showing a temperature detecting structure ofthe heat sink according to one embodiment of the present invention;

FIG. 38 is a block diagram showing a fan assembly controller accordingto another embodiment of the present invention;

FIG. 39 is a block diagram showing a fan assembly controller accordingto other embodiment of the present invention;

FIGS. 40A and 40B are charts showing a different rotational speedcontrol characteristic of the fan assembly;

FIG. 41 is an application of the heat sink according to the presentinvention disposed in a portable electronic apparatus;

FIG. 42 is an explanatory side view showing a mounted condition of theheat sink on the heat producing element in FIG. 41; and

FIG. 43 is a partially cutaway plan view showing a structure of akeyboard assembly in FIG. 41.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing the preferred embodiments, an explanation will begiven of the conventional heat sink.

FIG. 1 shows a conventional heat sink according to a prior art, forcooling a high temperature heat producing element. The heat sink H ismade of material such as aluminum having a good heat conductivity. Thetop face of the heat sink H has a set of radiating fins 6 shaped like acomb. The heat sink H is mounted to the surface of a heat producingelement 3 by adhesion or pressure, and is used in the circumstance wherea cooling air 10 is forcibly passed through the heat sink H. Heatproduced by the element 3 is transferred to the heat sink H and isabsorbed by it body or dissipated by the cooling air 10.

However, when the quantity of heat produced by the heat producingelement 3 rises in the conventional heat sink, the flow rate of airaround the heat sink H must be increased, thereby requiring a powerfulfan.

The powerful fan generally requires a large size fan blade or a highrotational speed. This results in increasing a fan installation spaceand noise.

Preferred embodiments of the present invention will be explained indetail with reference to attached drawings.

FIGS. 2 to 4B show a heat sink H according to the first embodiment ofthe present invention. The heat sink H comprises a heat sink body 1 madeof material such as aluminum having a good heat conductivity, and a fanassembly 2 such as a microfan for air-cooling the heat sink body 1.

The top of the heat sink body i is rectangular. The heat sink body 1comprises a fixing wall 4 whose back is mounted on a heat producingelement 3 with proper means described later, and a top plate 29supported by upright rectangular bars 7a protruding from four corners ofthe fixing wall 4, respectively. Ventilation paths 5 are formed betweenthe top plate 29 and the fixing wall 4 and open to the sides of the heatsink H.

The center of the top plate 29 has a circular hole serving as a fanreceiving recess 30 with the fixing wall 4 serving as the bottomthereof. A set of radiating fins 6 shaped like a comb are formed overthe top plate 29 and a set of radiating fins 4a also shaped like a combare formed over the fixing wall 4. The fixing wall 4 and top plate 29may be separate parts as shown in FIGS. 2 and 3, or be prepared as anintegrated part. (not shown).

The fan assembly 2 comprises a drive 2b such as a fan motor disposed incenter and a fan blade 2a fixed to a rotary shaft of the fan motor 2b.The fan assembly 2 is disposed in the recess 30. The fan assembly 2 maybe prefabricated and attached to the top plate 29 or to the fixing wall4. Alternatively, a stator of the motor 2a may be integral with thefixing wall 4. The fan assembly 2 may blow air toward the fixing wall 4,or draw air from the ventilation paths 5.

FIGS. 5 to 7 show a heat sink H according to the second embodiment ofthe present invention. The top of the heat sink H has four rectangularsections. A diagonally facing pair among the four sections is openedwith square openings 29a, and the other pair is closed with lids 29b.Comb-like radiating fins 4a are formed over the fixing wall 4, and thecenter of fixing wall 4 has a circular recess 4b for receiving the fanassembly 2. Note that the lids 29b are shown in FIG. 7 with hatching.Side walls are extended from the top plate 29 along the periphery of afixing wall 4. A pair of corners corresponding to the closed sectionswith the lids 29b have each an opening 29c which opens into an internalventilation path 5, and another pair of corners corresponding to theopen sections with the openings 29a have each a side wall 29d.

According to the heat sink H of the second embodiment constructed above,cooling air 10 is forcibly drawn through the openings 29a of the topplate 29 to cool the fixing wall 4 as indicated with arrow marks in theFIG. 7. The air is then discharged from the ventilation paths 5 throughthe openings 29c. The heated discharged air ascends along the side wallsof a heat sink body 1. This ascending heated air, however, neverre-enters the heat sink body 1 because the top face of the top plate 29above the opening 29c is closed with the lid 6. This results inimproving an overall cooling effect.

FIGS. 8 to 10 show a heat sink H according to a third embodiment of thepresent invention. In this embodiment, a heat sink body 1 comprises abase 7 and a cover 8 that are made of material such as aluminum having agood heat conductivity.

The top of the base 7 is rectangular. The base 7 has a set of radiatingfins 6 shaped like pins disposed upright around a center space where afan assembly 2 is disposed, and bars 7a protruding from four corners ofthe base 7, respectively. The top of each bar 7b has a threaded hole 31,and the cover 8 is fixed to the bars 7b with screws 32 engaging with thethreaded holes 31. A lead hole 33 and a lead groove 33a are formed atthe bottom of the base 7 as shown in FIGS. 8 and 10. A lead 34 from thefan assembly 2 is guided through the lead groove 33a after penetratedthrough the lead hole 33 and is connected to a pad of a printed board17.

The top shape of the cover 8 is identical to that of the base 7. At eachcorner of the cover 8, a screw hole 8b is formed to pass the screw thatengages with the threaded hole 31 of the base 7.

The cover 8 has a center hole 8a for receiving the fan assembly 2 havinga fan blade 2a. The periphery of the hole 8a is extended to form avertical partition 9.

The partition 9 surrounds the fan blade 2a when the cover is fixed onthe base 7, to increase the static pressure of cooling air 10 producedby the fan blade 2a.

FIGS. 11 to 12B show a heat sink H according to a fourth embodiment ofthe present invention. In this embodiment, the fan assembly 2 is mountedon the bottom face of the cover 8 to prevent a rise of temperature bythe heat conducted from the heat producing element 3 via the base 7 andto prolong the life of the fan motor 2b.

The cover 8 has a fan fixing part 35 at the center part of the bottomface thereof, and the fan assembly 2 is fixed by hanging from the fanfixing part 35. The fan assembly 2 is press fitted to the fan fixingpart 35 in this embodiment. The fan assembly 2 comprises a stator 36having a coil 36a on the outer surface, a shaft 38 vertically disposedat the center of the rotor 36 with a bearing 37, a rotor 39 fixed on theshaft 38 and having magnets 39a on the inner surface of the wall and fanblades 2a on the outer surface of the wall, and a printed circuit board40 to which a lead 34 is connected.

In FIG. 11, reference numerals 39b denotes a ring yoke, 36b denotes ayoke, 38a denotes a cut washer disposed on the shaft 38, and 38b denotesa spring for pressing the shaft 38 to the upper direction. Also in FIGS.11, 12A, and 12B, reference 41 denotes a opening for cooling air 10.When cooling air 10 is drawn from the opening 41 as shown by an arrow inFIG. 12A, and is discharged from the side wall of the base 7, it isdesirable to form a round corner R on the top end of the partition 9.The round corner R makes the speed of the drawing air constant anddecrease the generation of the noise due to the turbulent flow generatedby the sharp edge.

Next, the manner of fixing the cover 8 on the base 7 will be explainedhereinafter. One example to fix the cover 8 on the base 7 is to usescrews 32 as explained before. Other examples to fix the cover 8 on thebase 7 are shown in FIGS. 13 to 14B and in FIGS. 15 to 16B.

In the embodiment shown in FIGS. 13 to 14B, a fastening pin 11 having ahead 11a is disposed on each of the top faces of the bars 7a protrudingfrom four corners of the base 7. Correspondingly, a fastening hole 12 isdisposed at each of the four corners of the cover 8, and a side of thefastening hole 12 is open to the edge of the cover 8 through the guidechannel 12a. The guide channel 12a has a narrow part 12b.

In this embodiment, the cover 8 is set on the base 7 with entrances ofthe guide channels 12a facing the fastening pins 11 as shown by dottedline in FIG. 14A at first. Then the cover 8 is rotated to a directionindicated by an arrow in FIG. 14A and the pin 11 is led to be fastenedin the hole 12 after guided by the guide channel 12a and passed throughthe narrow part 12b. In this way, the cover 8 is fixed on the base 7.

In the embodiment shown in FIGS. 15 to 16B, each of the bars 7aprotruding from four corners of the base 7 has a circular arc convexface 13 and a guide groove 14 at an upper part thereof. The guide groove14 is cut at the base part of the circular arc convex face 13. A centerof each circular arc convex face 13 corresponds to the center of thebase 7. A hollow notch 13a is disposed on the middle part of eachcircular arc convex face 13. A curvature of the groove is smaller thanthat of the circular arc convex face 13 and a center of each groove 14corresponds to the center of the base 7.

Correspondingly, a projection 42 shaped like a triangle, is disposed ateach bottom face of the four corners of the cover 8 as shown in FIG. 15.The projection 42 has a circular arc concave face 15 and a fasteningsegment 16. The fastening segment 16 is protruded at the free edge ofthe circular arc concave face 15. A curvature of the fastening segment16 is smaller than that of the circular arc concave face 15 and a centerof each fastening segment 16 and a center of each circular arc concaveface 15 correspond to the center of the cover 8.

The circular arc concave face 15 faces to the circular arc convex face13, and the fastening segment 16 faces to the guide groove 14 when thecover 8 is fixed on the base 7. Further, a protruding portion 15a forfitting the hollow notch 13a of the base 7 is disposed on the middlepart of each circular arc concave face 15.

In this embodiment, the cover 8 is set on the base 7 with its protrudingportion 15a engaged to the guide groove 14 of the base 7 as shown bydoted line in FIG. 16A at first. Then the cover 8 is rotated to adirection indicated by an arrow in FIG. 16A and the protruding portion15a is led to be fastened in the hollow notch 13a after sliding on thecircular arc convex face 13. In this way, the cover 8 is fixed on thebase 7.

When an obstacle such as a printed board is disposed over the heat sinkH as constructed above and upper space of the cover 8 is very narrow,the air flow to the cooling air to the fan assembly 2 or from the fanassembly 2 is reduced due to an increase an air pressure loss, therebydecreasing the cooling capacity of the fan assembly 2 since the amountof air flowing to or from the fan assembly decreases.

FIGS. 17A to 20 are examples of the structure of the cover 8 when theheat sink H is uses in the above mentioned condition.

The cover 8 shown in FIG. 17A has cooling grooves 8c cut crosswise onthe top face thereof across the recess 8a. The cross section of thecooling grooves 8c in this embodiment is rectangular and each of thecooling grooves 8c is laid between the opposite sides of the cover 8.Note that the shape of the cross section of the grooves 8c is notlimited by rectangular. The other usable shape of the grooves 8c are,for example, a V shape as shown in FIG. 17B or a U shape as shown inFIG. 17C. The cooling grooves 8c disposed on the upper face of the cover8 can increase a space of the upper area of the cover 8.

FIG. 18A shows an air flow of the upper space of the cover 8 havinggrooves 8c as shown in FIG. 17A, and FIG. 18B shows an air flow of theupper space of the cover 8 having no grooves 8c when a shielding memberM is disposed over the cover 8. The heat sink 8 having no grooves 8c onthe top face of the cover 8 as shown in FIG. 18B is cooled only by thecooling air 10. Contrary to this, the heat sink 8 having grooves 8c onthe top face of the cover 8 as shown in FIG. 18A is cooled not only bythe cooling air 10 but a new cooling air 10' flowing in the grooves 8c.As a result, heat conducted from the bar 7a supporting the cover 8 isefficiently dissipated from the heat sink H by the cooling air 10'flowing in the grooves 8c on the top face of the cover 8. In this waythe grooves 8c assists cooling the cover 8.

FIG. 19A is a plan view of the cover 8 showing another example having aplurality of grooves 8c on the top face thereof, and FIG. 19B is anenlarged perspective view of a part X in FIG. 19A. In FIG. 19A, Thegrooves 8c are cut on the top face of the cover 8 radially from thecenter of hole 8a for receiving the fan assembly 2. The sectional shapeof the grooves 8c in this embodiment is V, but the shape thereof is notlimited by this embodiment. The sectional shape of the 8c mayrectangular or U, as explained before.

FIG. 20A is a plan view of the cover 8 showing other example having aplurality of radiating pins 8d on the top face thereof, and FIG. 20B isa side view of the cover 8 in FIG. 20A. The radiating pins 8d in thisembodiment is formed by decreasing the thickness of the cover 8 makingthe total thickness of the cover 8 equal to that of the cover 8 in FIG.8.

The cover 8 is cooled effectively by forming the radiating pins 8d onthe top face thereof decreasing the thickness of the cover 8 instead ofexcavating the cooling grooves 8c thereon. As a result, heat conductedfrom the bar 7a supporting the cover 8 is efficiently dissipated by thecooling air 10' flowing among the pins 8d on the top face of the cover8. In this way the radiating pins 8d assist the cooling of the cover 8.

The cover 8 having the cooling grooves 8c or the radiating pins 8d iseffectively cooled by the additional cooling air 10' when the cover 8 isdisposed in the condition where a little space is kept over the heatsink H by enlarging the space by the grooves 8c or the pins 8d. Thoughthis effect is small when the cover 8 having the cooling grooves 8c orthe radiating pins 8d is disposed in the condition where a large spaceis kept over the heat sink H.

FIG. 21 is a perspective assembly diagram showing a structure of a cover8 and a base 7 of the heat sink H, and a manner of assembling accordingto a fifth embodiment of the present invention. The heat sink H in thisembodiment uses the same base 7 explained as the third embodiment inFIG. 8, but the cover 8 is different from the third embodiment. Thecover 8 in this embodiment has radiating pins 8e on the bottom facethereof, though the the bottom face of the third embodiment is flat.

The radiating pin 8e in this embodiment is a circular pole and thediameter thereof is half the width of the radiating fin 6 projected onthe base 7. However, the shape of the radiating pin 8e is not limited bythe circular pole. The radiating pin 83 may be a triangular pole or asquare pole. The positions of the radiating pins 8e on the cover 8 areshown in FIG. 22. The radiating pins 8e projected into the center of thespace surrounded by the radiating fins 6 when the cover 8 is fixed onthe base 7 by the screws 32.

FIGS. 23A and 23B show a difference of an air flow of the cooling air 10between the cover 8 having radiating pins 8e and having no radiatingpins 8e on the bottom face thereof. The cooling air 10 flows straightpassing a side face of the radiating fin 6 when no pins are disposedtherebetween as shown in FIG. 23A. Contrary to this, when the pins 8eare disposed between the radiating fins 6, an air flow of the coolingair 10 is diffused by the radiating pin 8e and is passing not only aside face but also a front and a back faces of the radiating fin 6 asshown by reference 10" in FIG. 23B.

FIG. 24A is a diagram showing an air flow speed and an air flowdistribution characteristic. In FIG. 24A, black circles show thecharacteristic when the cover 8 has no radiating pins on the bottom facethereof, and black squares show the characteristic when the cover 8 hasthe radiating pins 8e on the bottom face thereof.

FIG. 24B is a diagram showing the relationship between air flow speedand thermal resistance. As is shown in FIG. 24B, an increment ΔRja ofthe thermal resistance Rja per unit voltage ΔV becomes smaller inaccordance with the increment of the air flow speed. Accordingly,cooling efficiency will be improved by distributing the cooling air 10from the area where a high speed cooling air is flowing to the areawhere a low speed cooling air is flowing.

In this way, the air flow distribution of the cooling air 10 becomesdiffuse and the air flow speed at the center part is decreased in theheat sink H of the fifth embodiment having the radiating pins 8d on thebottom face of the cover 8, as compared with the heat sink H having noradiating pins on the bottom face of the cover 8. As a result, an airflow speed of the cooling air 10 is increased at the side part of theheat sink H, thereby a cooling efficiency of the heat sink H of thefifth embodiment is increased.

FIG. 25 is a perspective assembly diagram showing a structure of a cover8 and a base 7 of the heat sink H, and a manner of assembling accordingto a sixth embodiment of the present invention. The fan assembly 2 isinstalled at the center of the heat sink H in the embodiment asexplained in FIGS. 8 to 10. Contrary to this, the fan assembly 2 isdisposed offset to one of the side of the heat sink H from the center inthis embodiment.

The base 7 has radiating fins 6, upright bars 7a at the four corners,and a windbreak wall 7b. The windbreak wall 7b is disposed at the sideto which the fan assembly 2 is offset, shielding the side between theupright bars 7a. FIG. 26 is a perspective plan view of the assembledheat sink H with the screw 32 having the cover 8 and the base 7 in FIG.25.

The reason why the fan assembly 2 is offset from the center of the heatsink H is to increase the cooling efficiency of the heat sink H bydecreasing the distance from the heat producing part and the heatradiating part. When the fan assembly 2 is disposed at the center of theheat sink H, the center of the heat producing element 3 cannot beexposed by the cooling air generated by the rotation of the fan blade2a. Contrary to this, when the fan assembly 2 is disposed offset fromthe center of the heat sink H, the center of the heat producing element3 can be directly exposed by the cooling air generated by the rotationof the fan blade 2a.

Further, an internal temperature rise of a bearing in the fan motor 2bof the fan assembly 2 is suppressed when the fan assembly 2 is disposedoffset from the center of the heat producing part. As a result, adeterioration of the grease in the bearing is suppressed to increase thelife and reliability of the fan assembly 2.

The existence of the windbreak wall 7b increases the cooling effect ofthe cooling air 10 flowing to the center of the heat sink H.

FIG. 27 is a perspective assembly diagram showing a structure of a cover8 and a base 7 of the heat sink H, and a manner of assembling accordingto a seventh embodiment of the present invention. The fan assembly 2 isdisposed offset to one of the side of the heat sink H from the centerthereof in the sixth embodiment as explained in FIGS. 25 and 26.Contrary to this, the fan assembly 2 is disposed offset to one of thecorner of the heat sink H from the center thereof in the seventhembodiment as shown in FIG. 27.

The base 7 has radiating fins 6, upright bars 7a at the four corners,and a windbreak wall 7b. One of the bar 7a to which the fan assembly 2is offset has a circular arc concave face and both sides thereof areextended to form a windbreak wall 7b. The windbreak wall 7b in thisembodiment also makes the flow of the cooling air 10 efficient. FIG. 28is a plan view of the assembled heat sink H with screws 32 having thecover 8 and the base 7 in FIG. 27;

FIG. 29 is a partially cutaway view in perspective of a modifiedembodiment of the base 7 in FIG. 27. In this embodiment, a space isformed by excavating an upper bottom face of the base 7 under theposition of the fan assembly 2 where no radiating fins 6 are disposed.The space has a first stage part 7c which is a shallow recess and asecond stage part 7d which is a deeper recess. The first stage 7c isformed under the fan motor 2b of the fan assembly 2 and under the halfpart of the trace path of the fan blade 2b, and the second stage 7d isformed under the other half part of the trace path of the fan blade 2b.

The first stage 7c and the second stage 7d may be formed on the base inthe sixth embodiment explained in FIGS. 25 and 26. The first stage 7cand the second stage 7d decreases the air pressure loss due to theexistence of the windbreak wall 7b by enlarging the space for thecooling air 10 to flow.

FIG. 30A is a plan view showing a modification of the base 7 in FIG. 27wherein a distribution of the radiating fins 6 are changed. Theradiating fins 6 are arranged densely around the center of the base 7and are arranged less densely around the side of the base 7. When thebase 7 has such an arrangement of the radiating fins 6, coolingefficiency is increased at the center part of the heat sink H by thenumber of radiating fins 6, and air pressure loss is decreased at theside of the heat sink H by the space between the fins 6. As a result,the cooling efficiency of the heat sink H will be increased withoutdecreasing the amount of air flow generated by the fan assembly 2installed in the heat sink H.

FIG. 30B is a sectional view taken on line Y--Y in FIG. 30A explainingthe structure of the stages 7c and 7c.

FIGS. 31A and 31B are a plan view and a side view showing a modifiedembodiment of the cover 8 according to the seventh embodiment of theheat sink H in FIG. 27. The cover 8 in this embodiment has a pluralityof radiating pins 8d on the top face thereof as explained in FIGS. 20Aand 20B embodiment. The radiating pins 8d in this embodiment are formedby decreasing the thickness of the cover 8 making the total thickness ofthe cover 8 equal to that of the cover 8 in FIG. 8. The cover 8 iscooled effectively with the radiating pins 8d on the top face thereof.

Note, the structure of making grooves 8c on the top face of the cover 8as explained in FIGS. 17A to 19B, and the structure making radiatingpins 8e on the bottom face of the cover 8 can be effectively applied tothe sixth and the seventh embodiment in which the fan assembly 2 isdisposed offset from the center of the heat sink H as explained above.Further, the arrangement of the radiating fins 6 as explained in FIG.30A is not limited by the embodiment, and the arrangement of theradiating fins 6 are changeable in accordance with the capacity of thefan assembly 2 and the shape of the fan blade 2a to increase the coolingefficiency.

FIGS. 32A and 32B show an example of a way of fitting the heat sink H tothe heat producing element 3 disposed on the printed board 17. In theembodiment as shown in FIG. 32A, shoes 43 for mounting the heat sink Hon the heat producing element 3 are soldered to the printed board 17.Each shoe 43 has an L-shaped cross section. A fixing spring bar 44 isattached to the shoes 43, to push the heat sink H against the heatproducing element 3.

FIG. 32B shows another example of a manner of fitting the heat sink H tothe heat producing element 3. A fixing clip 45 is formed as achannel-shape and has ends 45a. The heat sink H is mounted on the heatproducing element 3 by the pressing force of the fixing clip 45. Aplurality of the clips 45 are used to fix the heat sink H to the heatproducing element 3. Numeral 3a denotes an I/O pin of the heat producingelement 3.

Further, FIGS. 33A to 33F show another example of fitting the heat sinkH to the heat producing element 3 by using a heat sink fixture 28. Theheat sink fixture 28 has a level segment 26 having a fin hole 26a and aL-shaped pressing segment 27 extended from the level segment 26 as shownin FIG. 33C. The size of the fin hole 26a is as large as the pin-likeradiating fin 6 projected on the fixing wall 4 of the base 7 forpenetrating therein as shown in FIG. 33B.

The fin hole 26a of the heat sink fixture 28 is first penetrated by theradiating fin 6 with the pressing segment 27 bent. The heat sink fixture28 is then moved and pressed until the pressing segment 27 clips thebottom face of the heat producing element 3. After the fitting of theheat sink fixture 28, the heat sink H is mounted on the heat producingelement with pressure by the heat sink fixture 28.

Note that, the fin hole 26a provided on the level segment 26 of the heatsink fixture 28 may be be cut by a notch part 26b having a narrowerdistance than a diameter of the hole 26a as shown in FIG. 33D. When thefin hole 26a has the notch part 26b, it is easy to mount the heat sink Hon the heat producing element 3 by using the heat sink fixture 28, sincethe distance of the notch part 26b is enlarged by pressing the heat sinkfixture 28 to the direction of the radiating fin 6 as shown by an arrowin FIG. 33D.

Further, the the heat sink fixture 28 may have a parallel shape having aplurality of holes 26a or holes 26a with notch parts 26b as shown inFIGS. 33E and 33F.

In FIG. 10, the lead 34 is used to supply electricity to the fan motor2b of the fan assembly 2.

In FIG. 34, a power supply terminal 18 protrudes from the bottom side ofthe heat sink body 1. The terminal 18 is soldered to the printed board17, to supply electricity to the fan motor 2b of the fan assembly 2. Theterminal 18 may be attached to the printed board 17 according to asurface mounting technique or a through hole technique. Numeral 46 inFIG. 34 denotes internal circuit in the heat sink body 1, 47 denotes afan drive circuit, and 48 denotes a controller.

FIG. 32 shows still another example of a manner of fitting the heat sinkH to the heat producing element 3. In this embodiment, power supplyunits 19 such as pads and contacts are disposed on the heat producingelement 3 and connected to power source pads 17a of the printed board17. The heat sink H has power supply terminals 18, which are connectedto the power supply units 19, to supply electricity to the fan assembly2.

FIG. 36 shows a controller 48 for controlling the ON/OFF operation orrotational speed of the fan assembly 2. The controller 48 comprises afan driving circuit 47 and a switch 36. The fan driving circuit 47comprises a Hall element 49, a comparator circuit 50, a switchingelement 51 such as a switching transistor, and a coil 36a. In FIG. 37, atemperature sensor 20 such as a thermocouple or thermistor is embeddedin the fixing wall 4 of the heat sink body 1. The temperature sensor 20provides the switch 53 with an ON/OFF signal.

The switch 53 may comprise a transistor, a reed switch, or a relay.

FIG. 38 shows a rotational speed controller for the fan assembly 2. Therotational speed controller 54 is disposed between the switching element51 and the comparator circuit 50 of the fan driving circuit 47. Therotational speed controller 54 has an oscillator whose number ofoscillations corresponds to an output of the temperature sensor 20,thereby controlling the rotational speed of the fan assembly 2.

FIG. 39 shows a controller 48 for monitoring a rotational speed. Thecontroller 48 includes a rotational speed monitor circuit 52 having apulse generator. The pulse generator generates pulses in response to therotational speed of the fan assembly 2.

Note that the controller 48 may be disposed in the fan assembly 2, or ona separate board.

Further, above-described rotational speed control of the fan assembly 2can be realized in various ways. The control in FIG. 40A shows that thefan assembly 2 began to rotate when the temperature became apredetermined value T. The control in FIG. 40B shows that the fanassembly 2 rotates slowly when the temperature is lower than the value Tand the fan assembly 2 rotates faster when the temperature is equal orlarger than the value T.

FIGS. 41 to 43 show an application of the present invention where theheat sink H is used in a portable electronic apparatus such as anotebook-type personal computer. The portable electronic apparatus has aprinted board 17 and a drive unit 56 such as a floppy disk drive or ahard disk drive in its casing 21.

A heat producing element 3 such as an MPU (Micro Processing Unit) andother electronic parts 55 are mounted on the printed board 17. Theliquid crystal display unit 57 is also disposed on the casing and isable to swing as shown by an arrow in FIG. 41

A keyboard assembly 23 is disposed above the printed board 17 and isconnected to the printed board 17 by a flat cable 58. Reference 59denotes a connecter for connecting the flat cable 58.

The keyboard assembly 23 is, as is well-known to public, composed of aplurality of key tops 23a arranged in matrix above the housing thereofwhich is made of a synthetic resin. A reinforcing plate 22 made ofaluminum is disposed under the housing covering the full bottom facethereof for increasing the stiffness of the whole body.

The heat sink H for cooling the heat producing element 3 mounted on theprinted board 17 is formed by fixing the cover 8 on the base installingthe fan assembly 2 as shown in FIG. 42. A surrounding wall 24 isdisposed on the whole edge of the cover 8, and an upper edge of thesurrounding wall 24 is contacted to the bottom face of the reinforcingplate 22.

FIG. 43 shows a plurality of cooling air ventilation holes 25 disposedon the reinforcing plate 22 corresponding to the position of the fanassembly 2.

The cooling air 10 is forcibly drawn into the casing 21 through thecooling air ventilation holes 25.

As explained above, the heat sink H of the present invention has a goodcooling efficiency of the heat producing element, so that the heat sinkH of the present invention can be effectively used for the portableelectronic apparatus having a limitation of the internal space.

What is claimed is:
 1. A heat sink for cooling a heat producing element,comprising:a heat sink body including a base which is capable of beingmounted on the heat producing element; a fan assembly installed in aninternal space of the heat sink body, wherein the fan assembly includesa drive and fan blades fixed on a rotating shaft of the drive, wherein awidth of the heat sink body and the diameter of the fan assembly aresubstantially different, and wherein a region between the fan assemblyand the outer periphery of the heat sink body is defined; heat radiationfins disposed on a top face of the base within the region; and a coverclosing an upper portion of the region of the base.
 2. The heat sink asset forth in claim 1, wherein the cover includes an aperture forreceiving the fan assembly, a vertical partition extending downward froma periphery of the aperture surrounding the fan assembly.
 3. The heatsink as set forth in claim 1, further comprising radiation pins disposedon a bottom face or an upper face of the cover.
 4. The heat sink as setforth in claim 3, wherein the radiation pins are disposed on the bottomface of the cover so as to be positioned in the space surrounded by theradiation fins.
 5. The heat sink as set forth in claim 1, furthercomprising cooling grooves disposed on the upper face of the cover.